#include <stdio.h>
#include <math.h>
int main()
{
    double x1,x2,y1,y2;
    while(scanf("%lf%lf%lf%lf",&x1,&y1,&x2,&y2)!=EOF)
    {
        double x,y,n;
        x=(x1-x2)*(x1-x2);
        y=(y1-y2)*(y1-y2);
        n=sqrt((x+y));
        printf("%.2f\n",n);
    }
    return 0;
}